Technical Abstract:
In order to study the likely effects of global warming on rangeland and other ecosystems in the future, we developed arrays of infrared heaters that can produce uniform warming across 3-m-diameter field plots. The efficiency of the heaters was higher than that of the heaters used in most previous infrared heater experiments. Operating costs can be predicted from knowing this efficiency, desired degrees of warming, type of plant canopy, and site weather data, especially windiness. Four such arrays were deployed over plots of grass at Haibei, Qinghai, China and another at Cheyenne, Wyoming, USA, along with corresponding reference plots with dummy heaters. PID (proportional-integral-derivative) systems with infrared thermometers to sense canopy temperatures of the heated and reference plots were used to control the heater outputs. Over month-long periods at both sites, about 75% of canopy temperature observations were within 0.5 °C of the setpoint temperature differences between heated and reference plots. Electrical power consumption per 3-m-diameter plot averaged 58 and 80 kW-hr per day for Haibei and Cheyenne, respectively. However, the desired temperature differences were set lower at Haibei (1.2 °C daytime, 1.7 °C night) than Cheyenne (1.5 °C daytime, 3.0 °C night), and Cheyenne is a windier site. Thus, we conclude that these hexagonal arrays of ceramic infrared heaters can be a successful T-FACE (temperature free-air controlled enhancement) system for warming field plots of grazingland and other ecosystems.